Patient retention in care is critical to the success of programs funded by the President's Emergency Relief Plan for HIV/AIDS (PEPFAR). High levels of patient retention after first clinical contact contribute to the timely initiation of antiretroviral therapy (ART) and better health outcomes for patients. With the dramatic proliferation of cell phone use in Africa, telecommunications technology offers new opportunities to improve retention using a low-cost, culturally appropriate format. Our long-term research goal is to capitalize on the almost ubiquitous use of cellular phones to implement a sustainable mHealth service that improves health outcomes and supports patient engagement in care. In Kenya (WelTel Kenya1), a weekly short message service (SMS) text message led to improved ART adherence and viral load suppression. This study, WelTel Retain, will evaluate the effect of WelTel on retaining pre-ART patients in care and determine the cost- effectiveness of the intervention. Specific Aims: 1) To determine if the WelTel SMS intervention improves patient retention in the first stage of HIV care. 2) To determine whether the WelTel SMS intervention improves 12-month retention. 3) To evaluate the cost-effectiveness of the WelTel SMS intervention. Research Strategy: We will conduct a randomized controlled trial at the Kibera Community Health Centre in Nairobi, Kenya. Over one year, HIV positive individuals newly enrolling at the clinic will be recruited and randomly allocated to an intervention or control arm t a 1:1 ratio. Intervention arm participants will receive a weekly SMS 'check-in' to which they will be required to respond within 48 hours. An HIV clinician will follow-up and triage any problems that are identified. The control arm will receive standard of care. Patients will be followed for oe year, with a primary endpoint of retention in care at 12 months. Analysis: Enrolling 686 participants provides 80% power to detect a proportionate difference of 15% in the primary outcome (alpha=0.05). We will analyze data according to intention to treat principles. Chi-squared tests will be used for categorical outcomes; t-tests or Mann-Whitney U tests for continuous outcomes, and regression methods with appropriate interaction terms for subgroup analyses. Economic estimates include the incremental cost-effectiveness ratio per extra patient retained and the cost per life-year gained. Significance: The WelTel Retain study will contribute critical information on the effectiveness of an mHealth program to engage patients in care during the first year of HIV care. This research has the potential to demonstrate that the WelTel SMS intervention is an effective, feasible retention strategy, which can contribute significantly t the long-term success of PEPFAR-funded programs and towards a sustainable global HIV/AIDS response. PUBLIC HEALTH RELEVANCE: Engaging HIV-infected individuals in care is critical to the long-term success of programs funded by the President's Emergency Relief Plan for HIV/AIDS (PEPFAR). By retaining patients in care before they start treatment, the WelTel cell phone text messaging intervention could improve the health outcomes of people infected with HIV/AIDS and even reduce the risk of HIV transmission. Establishing the cost-effectiveness of WelTel could ultimately lead to health system efficiencies that save millions of dollars.